It is known that making a shoe in a production-line factory comprises a great number of operations requiring labor that is considerable and highly specialized for certain stations. These operations can be broken down into three main groups: cutting of the various constitutive pieces such as insoles and uppers; stitching phases; and assembly and finishing. Although the first two stages have been the object, so far, of thorough automation by use of improved machines, with relatively reliable operation and permitting good work rates, such as not been the case for the shoe assembly phases.
Briefly, these assembly operations and subsequent finishing of a bonded type shoe can be listed as follows on a traditional line where the base lasts are set and around which the various operations are performed: selection of the insole corresponding to the foot and size; centering and then attaching the insole on the last; curving the counters; assembly of the toes; assembly of the sides; assembly of the boxing (back part of the shoe); removal of the fastening clamps; successive roughing of the parts to be glued; gluing of the uppers mounted on the last; gluing of the outsole (generally obtained by injection of polyvinyl chloride or the like) and putting on the line; reactivation of the glue on the soles and uppers; positioning of the soles on the uppers; attaching, bonding under pressure; possibly cutting of false laces and removal of the shoe from its last; varnishing the shoe, generally by spray gun; drying; checking of the finished shoe; putting in boxes (generally made next to the line); stamping of the size and various distinctive markings; packaging; hooping; storage; and shipping.
In a shoe factory, such an assembly-finishing line requires the labor of about 15 persons, of which more than half are highly specialized and who have to make frequent manual interventions. This is done for an average hourly production of about one hundred pairs of shoes.
To try to remedy these drawbacks of long training of personnel, to reduce costs and to improve the manufacturing quality, it has already been proposed to supply different work stations and assure transfer and removal of semifinished or finished items by production lines allowing semiautomatic or automatic making of shoes. According to a first known group of transfer lines, essentially of Italian and Soviet origin, the line is made of a series of carriages operated for step-by-step advance along a given route, for example, polygonal, the carriages carrying lasts which, with some exceptions, are stationary and directed perpendicularly to the direction of the movement of the carriages; thus, the machine heads move along the line to come to work on the immobilized last. Various drawbacks have already been emphasized for this type of installation; in particular, there has been brought out the need of having relatively long periods of stopping for certain operations (for example, gluing or pressing) which leads to adopting advancement steps of long duration for the carriages and results in hourly productions that are considered insufficient, for example, on the order of 60 to 70 pairs of shoes. To remedy these drawbacks, there was then proposed a transfer line in which the last-carrying carriages are automated, i.e., provided with couplings-uncouplings and variable speed systems and where the lasts can be put into rotation in different directions as a function of the type of work machine. Thanks to its possibilities, such a line can make it possible to gain time in certain operations but, besides complexity in the technical embodiment of the carriages and their movement, it still requires the intervention of specialized labor for a series of manual adjustments, particularly depending on the size types.